The present invention is directed to magnetic storage devices and, in particular, to a magnetic read/write head carriage assembly for data storage devices using a flexible, doubled-sided magnetic recording medium.
Early magnetic storage devices for data processing systems made use of contact recording. This recording method was superceded to some extent after development of a magnetic head loading assembly in which the head was spaced away from the magnetic surface even during recording operations. This latter arrangement, which is currently used in high speed magnetic "hard disk" storage systems, permits the magnetic head to "fly" on a thin air layer over the recording medium so as to permit intimate interaction between the transducer and the magnetic surface. Contact recording has been used continuously, on the other hand, for less expensive, low speed magnetic storage devices such as magnetic tape and, more recently, floppy disk recording systems.
As is well known, a floppy disk is a rotatable, flexible magnetic disk, normally arranged in a cardboard dust cover. The so-called "floppy disk drive"--namely, a device for reading and recording information on such floppy disks--have come into widespread use for program and data storage because of their relatively low cost and small size notwithstanding a relatively rapid access to recorded information.
In the original floppy disk systems, the transducer structure generally comprised a single magnetic read/write head having a contact surface formed as a segment of a spheroid, or at least in a curved shape. The transducer was mounted on a movable carriage or base so that it could be accessed to different circumferential tracks on a floppy disk. On the opposite side of the disk, and also in contact with the disk was a pressure pad mounted on one end of a spring loaded arm. This arm, which was pivoted at its other end to the carriage base, was controlled by a solenoid to move into and out of contact with the floppy disk to permit data transfer operations to take place. The purpose of the pressure pad on the spring loaded arm was to exert a tracking force through the floppy disk against the single transducer.
Recently, floppy disk drives have been developed for floppy disks on which both sides are used for data storage and transfer operations: the so-called "double-sided" floppy disks. With these drives, a single low speed accessing mechanism continues to be employed but the storage capacity of the device is twice the capacity of a floppy disk drive using single-sided floppy disks. With these improved drives, the pressure pad is replaced by a second magnetic head so that two heads are arranged in a generally opposed relationship on opposite sides of the floppy disk, with only a slight offset in the two head gaps to avoid flux interaction.
This arrangement of opposed magnetic heads on a movable carriage assembly for double sided floppy disks is disclosed, for example, in the U.S. Pat. No. 4,151,573 to Tandon et al. and the U.S. Pat. No. 4,247,877 to Keller et al. These devices use a fixed magnetic head on one side of the floppy disk and a movable magnetic head on the opposite side. The movable head is gimballed on a pivoted, head support arm of low mass and high stiffness and urges the floppy disk against the fixed head with a light force. The force, which is applied by a spring that biases the support arm, is adequate to correct the deflections of the recording surface in a direction normal thereto, although this arrangement requires a slight penetration of the fixed head into the plane of the floppy disk.
The amount of force applied by spring biasing is not "critical;" that is, the floppy disk drive will operate properly provided that the force remains between certain minimum and maximum limits. However, a force which is substantially greater than that required for proper operation results in unnecessary and excessive wear of the magnetic head surfaces and the floppy disk itself.
In the carriage assembly disclosed in both of the above-mentioned patents, the tracking force is produced by a coil spring having a central, coiled portion and two end portions. One of the two end portions rests against the base of the carriage assembly and the other extends outward and applies a force to the head support arm. Neither of these arrangements provide any means for adjusting this spring force.
In the carriage assemblies disclosed in both of the above-mentioned patents the coil spring is located in a position behind and slightly above the head support arm. The spring is therefore exposed and venerable to damage or misadjustment when the magnetic read/write head carriage assembly is removed from the floppy disk drive enclosure for servicing.